1. Field of the Invention
The present invention relates to a vehicle drive system and particularly to its differential mechanism.
2. Description of the Prior Art
FIG. 1 shows a prior art differential mechanism having an outer housing 10 with a casing 12 rotatably supported therein on bearings 14. The casing 12 defines a chamber 16 and has a pair of diametrically opposed openings 18 therein. A pinion shaft 20, retained by a pin 22 in the casing 12 with one end thereof in each opening 18, transverses the chamber 16. A pair of pinion gears 24 are rotatably supported on the pinion shaft 20, one near each end, within the chamber 16. A pair of side gears 26 retained within the chamber 16 engage the pinion gears 24 to form a standard differential gear mechanism. The side gears 26 are axially aligned with the casing 12 and constrained by the differential gear mechanism to rotate in response to the pinion gears 24.
Each pinion gear 24 has a part-spherical end wall 24a and is supported thereat on a correspondingly shaped inner casing wall 12a. Similarly, each side gear 26 has a part-spherical end wall 26a where it is supported on a correspondingly shaped inner casing wall 12b. The inner casing walls 12a and 12b define a common sphere which has a radius of R and whose center coincides with the intersecting point 21 where the axis of rotation of the pinion shaft 20 intersects the axis of rotation of the casing 12 or the axis of rotation of the side gears 26. It follows, therefore, that the pinion gear end walls 24a and the side gear end walls 26a define a common sphere having a radius R.
The above described prior art differential mechanism is disadvantageous since it is bulky in the axial direction of the casing 12. That is, when designing the side gear, an increase in module of the side gear teeth tends to increase the axial size of the differential casing, resulting in an increased overall size of the differential mechanism.
The prior art differential mechanism is further disadvantageous since the side gears are rotatable about the pinion shaft before they are splined to axle shafts, resulting in difficulty when installing the differential mechanism on a car.